Wells are generally drilled into the ground or ocean bed to recover natural deposits of oil and gas, as well as other desirable materials that are trapped in geological formations in the Earth's crust. Wells are typically drilled using a drill bit attached to the lower end of a “drill string.” Drilling fluid, or mud, is typically pumped down through the drill string to the drill bit. The drilling fluid lubricates and cools the bit, and may additionally carry drill cuttings from the borehole back to the surface.
In various oil and gas exploration operations, it may be beneficial to have information about the subsurface formations that are penetrated by a borehole. For example, certain formation evaluation schemes include measurement and analysis of the formation velocity and seismic and/or acoustic properties. These measurements may be essential to predicting the production capacity and production lifetime of the subsurface formation.
Further, in addition to measuring and analyzing the formation velocity and seismic and/or acoustic properties, samples may also be taken of the formation rock within the borehole. For example, a coring tool may be used to take a coring sample of the formation rock within the borehole. The typical coring tool usually includes a hollow drill bit, such as a coring bit, that is advanced into the formation wall such that a sample, such as a coring sample, may be removed from the formation. Downhole coring operations generally include axial coring and sidewall coring. In axial coring, the coring tool may be disposed at the end of a drill string disposed within a borehole, in which the coring tool may be used to collect a coring sample at the bottom of the borehole. In sidewall coring, the coring bit from the coring tool may extend radially from the coring tool, in which the coring tool may be used to collect a coring sample from a side wall of the borehole.
As such, the coring sample may then be transported to the surface, in which the sample may be analyzed to assess, amongst other things, the reservoir storage capacity (porosity) and the permeability of the material that makes up the formation surrounding the borehole, such as the chemical and mineral composition of the fluids and mineral deposits contained in the pores of the formation and/or the irreducible water content contained in the formation.